The present energy shortfall which faces the world results from a number of conditions. First, and perhaps most pertinent, is the decrease in reserves of fossil type fuel in quantities that permit it to be produced indefinitely. In brief, the world's known oil reserves will prove to be adequate only for an indeterminate limited period of time. One form of relief from this shortage resides in the greater use of oil shale.
Oil shale comprises in essence a relatively impervious rock intermingled with an organic component known as kerogen. The hydrocarbon material can be released most readily through a heating of the shale to a sufficient temperature to thermally decompose the kerogen to an oil and a carbon residue. To most effectively utilize available heat, the shale is preferably crushed or otherwise reduced to a size most convenient to handle and to heat.
The oil segment which is removed from the shale is in many respects equivalent in characteristics to crude oil which is produced from any subterranean reservoir. Thus, the shale oil can be further distilled and otherwise handled to convert it into varying grades of petroleum products such as gasoline, heating oil, etc.
Toward exploiting this potential store of crude petroleum product, there is presently disclosed a novel, yet relatively inexpensive method for releasing and recovering shale oil from shale rock. The method embodies primarily the thermal treating of raw shale at relatively low temperature within a molten metal heating medium. Liquid crude, when thus released will rise to the surface of the heating pool and be readily recovered. Similarly, released gases are withdrawn for use in the process or disposed of leaving only residual shale rock.
It is therefore an object of the invention to provide a simple, yet inexpensive method for extracting oil from shale. A further object is to provide a relatively low temperature method for thermally treating oil shale to release kerogen or the hydrocarbon content thereof. Still another object is to provide a relatively high grade of shale oil which is released in liquid form from the shale, within a molten metal bath wherein the shale is thermally decomposed.
The process in brief as presently disclosed, envisions the thermal treatment of oil shale stocks which are determined to contain a sufficient amount of kerogen to warrant such treatment according to economic criteria. When proper conditions are maintained, virtually 100% of the Fischer assay value of the shale can be realized.
To achieve the best exposure of the raw kerogen containing rock, the latter is initially ground, crushed, or otherwise converted to a convenient size. Since the herein disclosed process relies heavily on the factor of a relatively short heating period, the size of the rock is preferably converted to a grade that will pass through a two inch sieve opening.
During the heating period the shale is immersed into a molten metal bath formed preferably of a lead composition which is at a temperature of approximately 950.degree. F. In such an environment, the kerogen is pyrolyzed. The liquid product floats onto the bath surface and can be then drained off, or otherwise removed.
The hot gases which are generated by the thermal decomposition of the shale can be recycled for use in preheating the shale prior to its immersion, or they can be otherwise disposed of.